Bone forming growth factors, such as bone morphogenetic protein (BMP) and transforming growth factor (TGF-β) have been widely investigated in orthopedics and tissue engineering with great success. These molecules stimulate bone cell growth and differentiation, and accelerate bone tissue regeneration [1, 2]. To prevent possible side-effects in non-target tissues, delivery of growth factors are performed in a controlled manner. For example, growth factors can be sequentially administered in a manner that mimics the time profile of the healing process [2-4].
Biomaterials, such as biopolymers [5-8], inorganic ceramics [9-18] and their compositions [19, 20], can act as reservoirs for deliverable protein and other bioactive molecules if they demonstrate a high capacity for protein adsorption while preserving the protein structure and biological activity over time. In addition to controlled protein delivery, carriers that are biocompatible with bone tissue can also serve as a scaffold for new tissue formation during normal tissue repair or healing. Furthermore, such biomaterials should be non-immunogenic and, in many cases, biodegradable once tissue regeneration is complete [2, 3]. Typically, biopolymers are not bioactive because they do not chemically bond to living bone. Inorganic bone replacement materials, including calcium phosphate ceramics [10, 11], bioglass and bioglass-ceramics [12], silica gel [13,14], and calcium phosphate cements [15-18], have been extensively investigated due to their excellent bioactivity with bone tissue. However, the adsorption capacity of protein on these carriers is limited to outer surface adsorption. Moreover, protein release from these materials displays a burst release (e.g., rapid release) due to the weak bonding between protein and the carriers.